Heroin’s Effects On The Brain

The dissection of heroin

The opium poppy has two main products; (1) poppy seeds, which are tasty and harmless, and (2) opium, which is bitter and addictive. As poppy seed pods ripen, they fill with codeine- and morphine-rich sap. Curiously, opium poppy plants are the only plants that produce codeine and morphine. About one week after the poppies flower, the sap is ripe and the morphine and codeine can be extracted, usually by scoring the sides of the seed pod.

In late afternoon the cuts are made, and the codeine-morphine-rich sap begins to seep out. As it dries overnight it oxidizes and turns dark brown. When the brown sap is harvested in the morning, cleaned and dried it becomes “Opium.” Most opium is about 10-14 percent morphine by weight. In places like Afghanistan and Mexico, where drug cartels thrive, morphine is mixed with acetic anhydride and boiled, to make heroin. Unlike morphine, which is used in hospitals to relieve pain, heroin is used to get high.

Actions of heroin

When heroin enters the brain it attaches to tiny proteins on nerve cells called receptors. Scientists have found three receptors that respond to heroin: mu (μ), kappa (κ) and delta (δ). These receptors are called opioid receptors and each type plays a different role. Since mu (μ), kappa (κ) and delta (δ) receptors are the first known opioid receptors, they are commonly referred to as the classical opioid receptors.

Heroin is an extraordinary drug because it binds to and activates μ-mu opioid receptors, which are the most prevalent and powerful opioid receptors in the brain, and the receptors most responsible for heroin’s effects.

6-monoacetylmorphine (6MAM)

Active metabolites of Heroin

After heroin is administered it starts traveling through the circulatory system. As soon as heroin touches blood it begins spontaneously metabolizing into 6-MAM. Ironically, 6MAM also metabolizes into morphine, and morphine metabolizes into M6G, and M6G into another chemical and so on and so forth. These newly metabolized chemicals are classified as either active metabolites or inactive metabolites. Active metabolites produce drug effects and inactive metabolites do not. The top-two active metabolites of heroin are 6-monoacetylmorphine (6MAM) and morphine. Both 6MAM and Morphine mimic the brain’s naturally occurring opioid neurotransmitters – endorphins.

Opioid receptors

The effects of 6MAM and Morphine depend upon how much heroin you take, how long you’ve been taking heroin and how you administer it. If heroin is injected, it acts faster and more intensely. If heroin is sniffed, it takes longer to reach the brain and reacts less intensely. Regardless if you sniff it, smoke it or shoot it, when 6MAM and Morphine permeate the brain they attach to mu (μ), kappa (κ) and delta (δ) opioid receptors. However, it’s the mu (μ) opioid receptors that produce the vast majority of drug-effects.

mu opioid receptor (MOR) – the mu receptor is the main “heroin receptor.” Throughout the body these are the most abundant opioid receptors and they’re directly responsible for heroins’ pleasurable effects, acute pain relief, physical dependence and addiction

Neurotransmitters

Neurotransmitters are chemicals within the nervous system that communicate information throughout our brain and body. They send signals from one neuron to another neuron. The brain uses neurotransmitters to tell your lungs to breathe, your heart to beat, and your stomach to digest. They also affect your mood, focus, and motivation.

Endorphins are the body’s natural neurotransmitters and they typically reduce pain or modulate mood. All addictive drugs mimic the actions of some neurotransmitter; in the case of heroin that neurotransmitter is probably endorphin. Ironically, the word “endorphin” is short for endogenous morphine, which means morphine made from within the body.

Cause of opiate addiction

The likelihood that a drug will lead to addiction is linked to the speed with which that drug promotes dopamine, the intensity of dopamine effects and the reliability that dopamine effects will occur.

Opiates like heroin, morphine and oxycodone are fast acting, produce a lot of dopamine and work close to 100% of the time. That’s why these three opiates in particular have been linked to several opiate addiction epidemics. The U.S. is currently coming out of an oxycodone epidemic and we’re currently in another heroin epidemic. The only morphine epidemic began during the Civil War and was quickly supplanted by heroin at the beginning of the 20th century.

Heroin’s effects on the brain

Heroin’s effects not only depend upon which type of opioid receptor it activates, but also the area of the nervous system in which they’re activated. Three of the most affected areas are the limbic system, which is in the forebrain; the brainstem, which is the bottom-most portion of the brain; and the spinal cord, which is a thin tube of nerves that extends from the base of the brainstem downward. These areas are not the only places you’ll find opioid receptors, but they have the most opioid receptors, and also produce the greatest effects.

Limbic System – When heroin attaches to opioid receptors within the limbic system it creates feelings of pleasure, relaxation, and contentment.

Brainstem – Underneath the limbic system is the brainstem. It connects the forebrain with the spinal cord. When heroin attaches to opioid receptors in the brain stem it slows breathing, inhibits coughing, and reduces pain.

Spinal Cord – When heroin attaches to opioid receptors within the spinal cord it reduces pain.

How heroin increases pleasure?

What typically happens is that 6MAM and a little morphine bind to and activate more mu, kappa and delta opioid receptors than any naturally occurring event. Therefore, heroin use ultimately results in a massive amplification of dopamine activity, which produces intense pleasure.

The sequence of events, from heroin use to feeling good, is quite simple. Heroin turns into 6MAM and a little morphine via the blood and liver, respectively. 6MAM and a little morphine enter the brain and behave like neurotransmitters and activate opioid receptors in the Ventral Tegmental Area (VTA). These activated receptors inhibit the release of GABA. Less GABA stimulates the release of dopamine. Dopamine travels from the VTA to the nucleus accumbens (NAc). Dopamine in the NAc attach to Dopamine receptors (D2) and the post-synaptic response is pleasure.

Neurons and Interneurons

What we’re looking at here are neurons. Your average neuron consists of a cell body, an axon and dendrites. The left picture shows a GABA axon terminal on top and a Dopamine dendrite on the bottom. The right picture shows a Dopamine axon terminal on top and an unspecified dendrite on the bottom. The space in between one neuron and the other is called a synapse. That is where signals from one neuron pass to another. Since the two neurons are not connected, the neuron on the top must release chemicals (neurotransmitters) from little vesicles (the bubbles in the picture) into the synapse.

This is where it gets interesting. Neurotransmitters have one of two possible functions, either to excite or inhibit a response. GABA neurotransmitters are considered inhibitory neurotransmitters. So after GABA neurotransmitters cross the synapse, they bump into and activate GABA receptors on Dopamine dendrites. The GABA receptors then send inhibitory signals to the Dopamine nucleus – to not release Dopamine. However, when heroin is consumed, the opposite occurs. But why does that happen?

The answer is absolutely fascinating. Heroin enters the body and quickly turns into 6-monoacetylmorphine (6MAM) and a little Morphine. Both 6MAM and Morphine bump into and activate opioid receptors on GABA neurons. Both 6MAM and Morphine act like inhibitory neurotransmitters themselves and suppress GABA neurons, to greater or lessor degree depending upon dosage. 6MAM and Morphine slow the rate of GABA release, which results in disinhibition of Dopamine. The left image up top shows inadequate GABA unable to completely suppress the release of Dopamine. The right image up top shows Dopamine traveling down the axon and into a different synapse, where it bumps into Dopamine receptors of a third neuron and around and around the brain it goes.

How long does heroin work?

6MAM has a short elimination half-life, which ranges between 6-25 minutes. Therefore, approximately 30 minutes after heroin is administered, over half of 6MAM molecules will have metabolized into heroin’s second metabolite, that is to say morphine. Morphine’s half-life is around 2.5 – 5 hours. Heroin’s half-life is considered the total of these two, and that means heroin’s half-life is a little less than 3 – 5.5 hours. The drug-effects of heroin last between one and two half-lives or 3 – 11 hours. The mean average being 7 hours.

Morphine activates opioid receptors longer than all other active metabolites of heroin. Therefore, the lingering drug effects are more connected to morphine, while the acute drug effects are more connected to 6MAM, but they do overlap.

Heroin adverse reactions

The most common adverse effects associated with the heroin use include nausea and vomiting, sedation, itchiness, urinary retention and constipation. Serious adverse effects frequently reported with heroin use include: respiratory depression, hypotension and delirium.

Heroin Overdose: Excessive heroin consumption may cause the brain to forget to breath. This may result in “hypoxia,” a medical condition in which there’s not enough oxygen in the blood to sustain life.

Heroin Dependence: Chronic heroin use causes physical dependence, which means that you are susceptible to withdrawal symptoms when you stop.

Heroin Addiction: Heroin use can also lead to addiction, which is a tenacious drive to get and use heroin despite negative consequences. It’s estimated that almost 1 in 4 (approx. 23%) new heroin users will become addicted.

Viruses: If you consider intravenous heroin use, then there are other health risks, such as contracting HIV, Hepatitis C, and Hepatitis B.

How does heroin affect the Gastrointestinal Tract

Heroin depresses brain centers that control major muscle groups. These muscles groups respond by slowing down the rate and depth of respiration, inhibiting coughs, and slowing down gastrointestinal motility. Heroin works in the GI Tract by reducing peristalsis, decreasing gastrointestinal secretions and relaxing longitudinal muscle in the colon as well as simultaneously/increasing contractions of the anal, esophageal and other sphincter muscles.